Érimón^[2] (ModernIrish:Éireamhón), commonly Anglicised asHeremon, son ofMíl Espáine (and great-grandson ofBreoghan, king of CelticGalicia), according to medieval Irish legends and historical traditions, was one of the chieftains who took part in theMilesian invasion of Ireland, which conquered the island from theTuatha Dé Danann, and one of the first MilesianHigh Kings.

Before coming to Ireland, he and his older brotherÉber Donn were joint rulers ofSpain. His great-uncleÍth made a peaceful expedition to Ireland, which he had seen from the top of a tower built by his fatherBreogan, but was killed by the three kings of the Tuatha Dé Danann,Mac Cuill,Mac Cecht andMac Gréine, and in revenge the Milesians invaded in force, with Érimón and Éber Donn in command. They defeated the Tuatha Dé Danann in the Battle ofTailtiu. Éber Donn had been killed, and the High Kingship was divided between Érimón in the north and his younger brotherÉber Finn in the south.

A year after the Battle of Tailtiu, Éber Finn became unhappy with his half and fought a battle with his brother at Airgetros, a district along the River Nore where counties Kilkenny and Laois now meet. There Éber Finn lost and was killed. Érimón became sole ruler of Ireland and built his capital at Ráth Oinn (later site ofRathdown Castle, on the east coast near modernGreystones). He appointed kings of the four provinces. He gaveLeinster toCrimthann Sciathbél of theFir Domnann;Munster to the four sons of Eber Finn,Ér, Orba, Ferón and Fergna;Connacht toÚn andÉtan, sons of Uicce; andUlster toEber mac Ír. During this time theCruithne settled in Ireland. He ruled for fourteen, fifteen or seventeen further years, after which he died at Airgetros, and was succeeded by his sons Muimne, Luigne and Laigne, ruling jointly.^[3]

Geoffrey Keating dates his reign from 1287 to 1272 BC,^[4] theAnnals of the Four Masters from 1700 to 1684 BC.^[5]

Some philologists believe Érimón and Zarathustra’s mythological Aryaman character who gives their name to Iran are cognates.^[6] Georges Dumèzil retracted his initial view on this matter.^[7] However, the idea remains seductive to some commentators,^[8] on the basis of the coincidence of the similar sound between the two names, that they both are mythological founders of two separate great Indo-European cultures, the inclusion of the M-N- sound in their respective names, and the fact that many of the great Indo-European cultural traditions’ founders share the same M-N- laden moniker.

Érimón had two wives, Odba, mother ofMuimne, Luigne and Laigne, whom he left behind in Spain, and Tea, mother ofÍriel Fáid, who accompanied him to Ireland, and died there. Tea was a daughter ofLugaid^[9] and gave her name toTara, where she was buried – theLebor Gabála Érenn explains itsOld Irish nameTemair as "Tea mur", "Tea's Wall". Through his son, Íriel Fáid, Érimón was the progenitor of the Heremonians and provided many High Kings of Ireland. Kinship groups of Irish Gaels which are classified as Heremonians were most powerful inConnacht,Osraige,Leinster and parts ofUlster and include theConnachta,Uí Néill,Clan Colla,Uí Maine,Laighin,Dalcassians and theÉrainn.^[1]

The Red Lion of Heremon features inIrish heraldry andScottish heraldry as a device in the coat of arms of many of Heremon's claimed descendants, including:

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  O'Neill
• 
  O'Melaghlin
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  MacGeoghegan
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  Magawly
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  O'Kearney
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  McCaughey
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  Kavanagh
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  Donegan
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  O'Dwyer
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  MacMahon
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  Dunkeld
• 
  MacDuff

• Rathbeagh

• Legendary High Kings of Ireland
• Founding monarchs in Europe

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